diff --git a/agent/model_metadata.py b/agent/model_metadata.py
index 24ebf34657..01204e8aa6 100644
--- a/agent/model_metadata.py
+++ b/agent/model_metadata.py
@@ -164,6 +164,8 @@ _URL_TO_PROVIDER: Dict[str, str] = {
     "openrouter.ai": "openrouter",
     "inference-api.nousresearch.com": "nous",
     "api.deepseek.com": "deepseek",
+    "api.githubcopilot.com": "copilot",
+    "models.github.ai": "copilot",
 }
 
 
@@ -788,8 +790,12 @@ def get_model_context_length(
         if cached is not None:
             return cached
 
-    # 2. Active endpoint metadata for explicit custom routes
-    if _is_custom_endpoint(base_url):
+    # 2. Active endpoint metadata for truly custom/unknown endpoints.
+    # Known providers (Copilot, OpenAI, Anthropic, etc.) skip this — their
+    # /models endpoint may report a provider-imposed limit (e.g. Copilot
+    # returns 128k) instead of the model's full context (400k).  models.dev
+    # has the correct per-provider values and is checked at step 5+.
+    if _is_custom_endpoint(base_url) and not _is_known_provider_base_url(base_url):
         endpoint_metadata = fetch_endpoint_model_metadata(base_url, api_key=api_key)
         matched = endpoint_metadata.get(model)
         if not matched: